1. Field of the Invention
The present invention relates to an air conditioning system and a control method thereof, and more particularly to an air conditioning system and a control method thereof which are capable of compensating for pressure drop of a refrigerant in a line connecting an outdoor unit and one or more indoor units.
2. Description of Related Art
Generally, air conditioning systems are used to cool or heat confined spaces, for example, rooms in a building. In such an air conditioning system, a refrigerant is circulated between an indoor unit and an outdoor unit such that the refrigerant absorbs ambient heat while evaporating from a liquid phase, and discharges the absorbed heat while condensing from a gaseous phase. In accordance with such characteristics of the refrigerant, the air conditioning system performs a cooling or heating operation.
In a typical air conditioning system, one indoor unit is installed for one outdoor unit. However, recently, the use of an air conditioning system in the form of a multi-system air conditioner has increased. In a multi-system air conditioner, a plurality of indoor units having various structures and various capacities are connected to one or more outdoor units, in order to perform a cooling or heating operation for an area where there are a plurality of separated spaces, as in a school, a company, or a hospital.
FIG. 1 is a block diagram illustrating the configuration of a multi-system air conditioner. For the convenience of explanation, the situation, in which the air conditioning system is used to cool spaces, will be first described.
The conventional multi-system air conditioner includes an outdoor unit 10 and a plurality of indoor units 20 connected to the outdoor unit 10. The outdoor unit 10 includes a compressor for compressing a gaseous refrigerant emerging from the indoor units 20 after performing heat exchange in the indoor units 20, and an outdoor heat exchanger for transferring heat in the refrigerant to ambient air. Each indoor unit 20 includes an indoor heat exchanger. The conventional multi-system air conditioner also includes a gaseous refrigerant line 30 and a liquid refrigerant line 40 connected between the outdoor unit 10 and the indoor units 20, to transfer the refrigerant while in a gaseous phase and a liquid phase, respectively.
The multiple indoor units 20 of the above-mentioned multi-system air conditioner are connected to the outdoor unit 10 via lines branched from the outdoor unit 10, and are installed in one or more stories of a multi-story building, or in other separated spaces. In this multi-system air conditioner, the refrigerant is sent from the outdoor unit 10 to each indoor unit 20 via the gaseous refrigerant line 30 after being compressed in the outdoor unit 10 and returned to the outdoor unit via the liquid refrigerant line 40.
In accordance with the above-mentioned arrangement, the refrigerant circulating through the multi-system air conditioner forms a repetitive cycle of evaporation—compression—condensation—expansion, in which the refrigerant absorbs heat in the indoor heat exchanger of each indoor unit 20, through an evaporation process, is compressed in the compressor of the outdoor unit 10, is condensed, and is then expanded through an expansion valve.
When the air conditioning system is used to heat rooms, the cooling cycle of the air conditioning system is reversed. That is, the refrigerant absorbs heat in the heat exchanger of the outdoor unit 10, and discharges the absorbed heat through the heat exchanger of each indoor unit 20 installed in a room. Thus, the air conditioning system can absorb heat from a low-temperature area, namely, the outdoors, and can use the absorbed heat in order to heat rooms. When the absorbed heat is insufficient to heat rooms, it may be possible to heat the rooms using an electric heater, together with the absorbed heat.
In either case, the gaseous refrigerant line 30 and the liquid refrigerant line 40, which connect the outdoor unit 10 and the indoor units 20, are provided. However, when the refrigerant is evaporated in accordance with an evaporation function, there may be a problem in that a pressure drop of the evaporated gaseous refrigerant occurs in the gaseous refrigerant line 30, through which the gaseous refrigerant flows.
In an air conditioning system such as a multi-system air conditioner, when the number of indoor units 20 connected to one outdoor unit 10 increases and/or the distance of each indoor unit 20 from the outdoor unit 10 increases, the length of the refrigerant line correspondingly increases. However, such an increase in the length of the refrigerant line causes an increase in the resistance applied to the refrigerant flowing through the refrigerant line. In particular, the internal pressure of the gaseous refrigerant line 30, through which a gaseous refrigerant flows, may drop.
The performance of the air conditioning system is proportional to the circulation flow rate of the heat-exchangeable refrigerant. Consequently, a pressure drop of the gaseous refrigerant in the gaseous refrigerant line 30 decreases the circulation flow rate of the refrigerant, thereby degrading the efficiency and performance of the refrigerant cycle. Furthermore, since the refrigerant cannot smoothly flow, noise may be generated in the refrigerant line.